let promise = new Promise((r, j) => {
    r('123')
})

promise
.then(fn1, fn2)
.then(fn3, fn4)

// promise
// .then(fn3, fn4)
// .then(fn1, fn2)


function fn1(res) {
    console.log('fn1', res)
    return new Promise((r, j) => {
        r('fn1 返回值')
    })
}
function fn2(res) {
    console.log('fn2', res)
    return new Promise((r, j) => {
        r('fn2 返回值')
    })
}
function fn3(res) {
    console.log('fn3', res)
    return new Promise((r, j) => {
        r('fn3 返回值')
    })
}
function fn4(res) {
    console.log('fn4', res)
    return new Promise((r, j) => {
        r('fn4 返回值')
    })
}